"It's official; dieting does make us depressed," laments the Mail Online, following the publication of a study on how losing weight affects a person’s mood.

Healthy Diet, Healthy Mind

A study of 1,979 overweight and obese people found that those who lost 5% of their bodyweight were nearly twice as likely to feel some symptoms of depression, compared with those who stayed a similar weight.

As expected, it found that losing weight reduced the risk of high blood pressure and lowered levels of fats in the blood, thereby benefiting their health.

However, people who lost weight over the course of the four-year study were 78% more likely to report feelings of being in a “depressed mood” compared with participants whose weight remained stable.

Despite the headlines, the study did not prove that weight loss caused a depressed mood, as the weight loss and the change in mood occurred over the same time period.

Further studies will be needed to establish whether weight loss can cause a depressed mood.

How participants lost weight was not reported, so we can’t tell if they followed any particular diet or physical activity regime that lowered their mood. As a result, the Mail Online’s headline of “Dieting DOES make us depressed – even though we're healthier” is not justified, based on this study.

Overall, this study suggests that spontaneous weight loss is beneficial for people’s health, but the psychological effects are less clear – and potentially negative. These results may be worthy of further investigation.

Where did the story come from?

The study was carried out by researchers from University College London (UCL). It was funded by the National Institute on Aging and a consortium of UK government departments coordinated by the Office for National Statistics (ONS).

The assertion that it is “official” that “Dieting DOES make us depressed – even though we're healthier” is not justified based on this study. This is because the study did not assess depression, and we have no evidence that the people went on a diet to lose weight. They could equally have eaten the same foods as they usually do and increased their exercise a little. How the people lost weight was not reported.

What kind of research was this?

This was a cohort study looking into the physical and psychological effects of weight loss in overweight or obese adults aged 50 years or older.

The researchers flag up how weight-related diseases, such as diabetes and cardiovascular disease, are on the rise, with health organisations worldwide advising overweight and obese adults to reduce their body weight. The physical benefits of weight loss are well established, but the psychological benefits are less clear.

Studies on individuals have found positive psychological benefits, but large population studies have not. This, the authors thought, might be due to the inclusion of healthy-weight individuals who have never had to lose weight.

The research group decided to examine changes following weight loss in a cohort of exclusively overweight/obese adults, to see whether there were psychological gains masked in previous studies.

What did the research involve?

The team collected information from 1,979 overweight and obese adults (BMI equal to or higher than 25kg/m2; age 50 and above), free of long-standing illness or clinical depression at baseline, recruited from the English Longitudinal Study of Ageing. During a four-year period, researchers monitored their weight, blood pressure and the level of lipids (fatty substances) in their blood, as well as their mood and wellbeing.

The main analysis looked at whether there were any differences in psychological measures between those who lost weight, compared to those who didn’t.

Participants were grouped according to four-year weight change:

participants losing 5% or more in weight

participants gaining 5% or more

participants whose weight didn’t move up or down by more than 5%

The main measures of psychological wellbeing used were:

depressed mood (eight-item Center for Epidemiologic Studies Depression score four or more, includes questions like "Over the last week have you felt sad?" with yes/no response options)

low wellbeing (scoring less than 20 on the Satisfaction With Life Scale score)

The main analysis controlled for the effects of age, sex, wealth, weight loss intention, major life events that might be stressful, and impact on weight and wellbeing, as well as their health at the start of the study.

What were the basic results?

Around 15% of people in the overweight and obese group lost 5% or more of their bodyweight over the four-year period, and a similar proportion gained 5% or more. The vast majority, however, remained a similar weight.

Psychological wellbeing deteriorated (increased rates of depressed mood and low wellbeing) between the start of the study and follow-up across all three weight-change groups.

People who lost 5% or more of their body weight were nearly twice (78%) as likely to report feelings of a depressed mood compared to those whose weight remained stable (odds ratio [OR] = 1.78 [95% CI 1.29-2.47]). When this was adjusted for the effect of life events the odds ratio fell slightly to OR 1.52, 95% CI 1.07-2.17).

The proportion of adults with low wellbeing also increased more in the weight loss group, but the difference was not statistically significant (OR = 1.16, 95% CI 0.81-1.66). In some of the subsequent analysis, weight loss was significantly linked to a lower wellbeing.

The same results were observed when the researchers accounted for illness and life stress during the weight loss period.

How did the researchers interpret the results?

The researchers concluded that “weight loss over four years in initially healthy overweight/obese older adults was associated with reduction in cardio-metabolic risk, but no psychological benefit, even when changes in health and life stresses were accounted for. These results highlight the need to investigate the emotional consequences of weight loss”.

Conclusion

This study indicates that overweight or obese people aged over 50 who lose more than 5% or their body weight over four years reap physical benefits, but do not appear to reap psychological benefits; in fact they had worse ratings of “depressed mood” than the people who maintained a stable weight.

The study population is broadly representative of the UK population over the age of 50, and the analysis was appropriate. However, there are limitations to consider when interpreting these findings.

Firstly, the reasons behind the weight loss were not documented – e.g. spontaneous increase in exercise or referral from GP to a weight loss programme. Some reports in the media suggested the low mood might be due to the punitive diets some people might be trying in order to lose weight. However, without more information on the nature and cause of the weight loss, this is pure speculation.

The researchers usefully highlighted the three possible explanations of their results – all of which are plausible, and none can be completely confirmed or dismissed based on this study alone.

weight loss causes depressed mood

depressed mood causes weight loss

weight loss and depressed mood share a common cause

In terms of point one, the authors note that long-term maintenance of weight loss is notoriously hard, with many people failing to keep the weight off. They speculate that this may be a sign of personal costs, strains and difficulties in achieving this, which could affect a person’s mood. This suggests a plausible but unproven mechanism by which weight loss could be a psychological challenge influencing mood and wellbeing.

In terms of point two, depressed mood may cause weight loss directly or indirectly through changes in appetite or level of physical activity. The design of the study means it was not possible to establish which came first: weight loss or depressed mood.

In terms of point three, some of the obvious common causes of weight loss and low mood include major life events, such as separation or divorce from a partner, or developing an illness – both of which were covered in the analysis. Even though these factors were partially ruled out as a common cause, we cannot rule out other factors as a potential explanation for the results.

Like all cohort studies, some factors may not have been accounted for or may not have been properly measured. A potential confounder in the present study, as noted by the authors, was the presence of underlying disease causing both weight loss and depressed mood. The analysis adjusted for limiting long-standing illness, but this was self-reported rather than diagnosed, so may not be a wholly accurate measure of health status.

Overall, this study suggests that spontaneous weight loss is beneficial for people’s health, but the psychological effects are less clear, and potentially negative. These results may be worthy of further investigation.